This invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a MOSFET gate insulating film in a semiconductor device using two types of power supply voltage in a single chip and a method of manufacturing the same.
As integrated circuits are being required to operate much faster, the gate electrode length of a MOSFET grows finer at an increasingly rapid pace. By 2000, the advent of an integrated circuit using MOSFETs with a gate electrode length on the order of about 0.15 xcexcm to 0.1 xcexcm is expected. In such a fine MOSFET, it is expected that the power supply voltage to bring out the optimum performance might more frequently differ from the power supply voltage determined by the interface with another device on the outside. For example, this corresponds to the following case: use of a power supply voltage of 2.5V is preferable to the interface with an external device, whereas use of a power supply voltage of about 1.8V is preferable to operating the relevant integrated circuit at high speed.
Another problem in miniaturizing MOSFETs arises from making the gate insulating film thinner. Specifically, the gate insulating film must be made thinner as the gate electrode length grows finer. In this case, when the electric field applied to the thin gate insulating film has reached 5 MV/cm or higher, the insulating film is more liable to be broken, decreasing the reliability.
For this reason, a semiconductor device required to operate at higher speed has employed such a structure including MOSFETs with different gate insulating films formed in a single chip and selectively using the MOSFETs with the gate insulating film thickness suitable for each power supply voltage.
Still another problem in making the gate insulating film thinner arises from: when p-type polysilicon is used for the gate electrode of a p-channel MOSFET with a fine gate length, p-type impurities, such as boron, included in the polysilicon pass through the thinner gate insulating film in various thermal processes carried out in the manufacturing processes and diffuse throughout the substrate, which degrades the controllability of the threshold voltage. It is known that use of material including a trace of nitrogen for the gate insulating film is effective in dealing with the problem. For example, it is desirable that oxynitride should be used for a gate insulating film whose thickness is 6 nm or less.
Next, using FIG. 1 and FIGS. 2A to 2D, a conventional semiconductor device and a method of manufacturing the semiconductor device will be explained.
As shown in FIG. 1, element isolating regions 12 have been formed at the main surface of a silicon (Si) substrate 11. In the element regions electrically separated by the element isolating regions 12, diffused layers 13 and 14 acting as source/drain regions are formed. A gate insulating film 15 is formed on the silicon substrate 11 between the source/drain regions 13. On the gate insulating film 15, a gate electrode 16 is formed, thereby constructing a MOSFET Q1. A gate insulating film 17 is formed on the silicon substrate 11 between the source/drain regions 14. A gate electrode 18 is formed on the gate insulating film 17, thereby constructing a MOSFET Q2.
The MOSFET Q1 constitutes an internal circuit. In the p-channel MOSFET in area A in which the MOSFET Q1 has been formed, p-type material, such as boron-doped polysilicon, is used for the gate electrode 16. In contrast, the MOSFET Q2 formed in area B constitutes a circuit for exchanging signals and data with an external device. The MOSFET Q1 formed in area A operates on about 1.8V lower than MOSFET Q2 formed in area B and the dimension (gate length) of, for example, the gate electrode is 180 nm. In the MOSFET Q1, the gate insulating film 15 requires a thickness of about 4 nm to provide the optimum performance. In contrast, because an external power supply voltage of 2.5V is applied to the MOSFET Q2 formed in area B, the gate insulating film 17 needs a thickness of about 6 nm. An oxynitride film is used as the gate insulating films 15 and 17.
The semiconductor device of FIG. 1 is formed by the processes shown in FIGS. 2A to 2D. First, as shown in FIG. 2A, element isolating regions 12 are formed in a silicon substrate 11. Then, impurities for controlling the threshold voltage of a MOSFET are introduced into the main surface of the silicon substrate 11.
Thereafter, as shown in FIG. 2B, to become a gate insulating film 17, oxynitride is deposited on the main surface of the silicon substrate 11. The oxynitride film has a thickness of, for example, about 5 nm. Following that, a resist pattern 19 is formed as a mask on the oxynitride film 17 in area B by, for example, photoetching techniques.
Next, after the oxynitride film 17 on area A has been removed, another oxynitride layer is deposited as a gate insulating film 15 to a thickness of, for example, 4 nm. In this case, the oxynitride film 17 on area B is subjected to another oxidation, which forms a gate insulating film 17 of about 6 nm in thickness (see FIG. 2C).
Thereafter, as shown in FIG. 2D, polysilicon 20 is deposited on the gate insulating films 15 and 17 to a thickness of, for example, about 200 nm. The polysilicon film is patterned by photoetching techniques, thereby forming gate electrodes 16 and 18.
Then, impurity ions are implanted into the silicon substrate 11. The resulting silicon substrate is then activated by rapid thermal annealing at about 1000xe2x96xa1, thereby forming a diffused layer to act as the source/drain regions 13 and 14 of each of the MOSFETs Q1 and Q2. This completes a semiconductor device as shown in FIG. 1.
In the semiconductor device formed as described above, use of an oxynitride film for the internal circuit MOSFET Q1 using the gate insulating film as thin as about 4 nm prevents p-type impurities from diffusing from the gate electrode 16 into the silicon substrate 11. In the manufacturing processes, however, the MOSFET Q2 interfacing with an external device using the gate insulating film 17 as thick as about 6 nm has also a structure using an oxynitride film. In heat treatment at about 1000xe2x96xa1, the gate insulating film of about 6 nm in thickness does not necessarily need oxynitride from the viewpoint of the diffusion of p-type impurities from the gate electrode 18 into the silicon substrate 11. Conversely, use of oxynitride causes the problem of decreasing the current driving capability of the MOSFET Q2 due to the appearance of an interface level. Therefore, use of oxynitride is unfavorable from the standpoint of making the operation speed of the semiconductor device faster.
In the conventional semiconductor device and the method of manufacturing the semiconductor device, since an oxynitride film has been used as all the gate insulating films in an LSI requiring two or more types of power supply, this has caused the problems of decreasing the current driving capability and operation speed of the MOSFET.
A first embodiment of the present invention is to provide a semiconductor device capable of not only minimizing a decrease in the current driving capability of a MOSFET but also making its operation speed faster in an LSI requiring two or more types of power supply.
A second embodiment of the present invention is to provide a method of manufacturing a semiconductor device capable of not only minimizing a decrease in the current driving capability of a MOSFET but also making its operation speed faster in an LSI requiring two or more types of power supply.
The first object of the invention is accomplished by providing a semiconductor device comprising: a first circuit which is integrated in a semiconductor chip and operates on a first voltage and which includes a transistor whose gate insulating film is made of SiO2; and a second circuit which is integrated in the semiconductor chip and operates on a second voltage lower than the first voltage and which includes a transistor whose gate insulating film is made of an oxynitride film of nitrogen-added SiO2, wherein the gate electrodes of the p-channel transistors among the transistors are made of a p-type conductivity material.
It is preferable that the gate insulating film used in the transistor constituting the first circuit has a thickness of 5 nm or more and the gate insulating film of the transistor constituting the second circuit has a thickness of less than 5 nm.
Furthermore, the first object of the invention is accomplished by providing a semiconductor device integrated in a single chip and operating on a first and a second power supply voltage, comprising: an interface circuit which operates on the first power supply voltage and exchanges signals and data with an external device and which includes a transistor whose gate insulating film is made of SiO2; and an internal circuit which operates on a second power supply voltage lower than the first power supply voltage and which includes a transistor whose gate insulating film is made of an oxynitride film nitrogen-added SiO2, wherein the gate electrodes of the p-channel transistors among the transistors are made of a p-type conductivity material.
The semiconductor device preferably has the following characteristics:
(a) The gate insulating film used in the transistor constituting the interface circuit has a thickness of 5 nm or more and the gate insulating film of the transistor constituting the internal circuit has a thickness of less than 5 nm.
(b) Each of the gate electrodes of the transistor in the interface circuit and the transistor in the internal circuit includes at least one of polysilicon, a stacked structure of polysilicon and silicide, a stacked structure of polysilicon and metal, a stacked structure of polysilicon and TiN, and a stacked structure of polysilicon, metal, and TiN.
(c) The p-type conductivity material included in the gate electrode of the p-channel transistor includes either boron or BF2.
(d) The concentration of nitrogen included in the oxynitride film is preferably 1.3 atm % or less, when the p-type conductivity material included in the gate electrode of the p-channel transistor is boron.
(e) The concentration of nitrogen included in the oxynitride film is preferably 1.2 atm % or less, when the p-type conductivity material included in the gate electrode of the p-channel transistor is BF2.
With the above configuration, because a pure oxide film (SiO2) is used for a MOSFET operating on a high voltage and requiring a thick gate insulating film and an oxynitride film is used for a MOSFET operating on a low voltage and requiring a thin gate insulating film, the characteristic of, for example, not only the MOSFET constituting the first circuit (interface circuit) to which an external power supply voltage is directly applied is prevented from deteriorating because of the influence of nitrogen, but the problem of penetration of boron through, for example, the MOSFET constituting the second circuit (internal circuit) to which the internal power supply voltage is applied is avoided. This makes it possible to minimize a decrease in the current driving capability of the MOSFET and make the operation speed faster in an LSI requiring two types of power supply.
When the gate insulating film used in the MOSFET constituting the first circuit is formed thicker than 5 nm and the gate insulating film of the MOSFET constituting the second circuit is formed thinner than 5 nm, this suppresses the problem of deterioration of the characteristic because of the influence of nitrogen and the problem of penetration of boron more effectively.
The second object of the invention is accomplished by providing a method of manufacturing a semiconductor device where a first circuit operating on a first voltage and a second circuit operating on a second voltage lower than the first voltage are formed in a single chip and a p-type conductivity material is used for the gate electrode of a p-channel transistor constituting the second circuit, comprising: the step of forming an oxynitride film of nitrogen-added SiO2 as the gate insulating film of a transistor constituting the second circuit; the step of forming the gate electrode material layer of the transistor constituting the second circuit on the oxynitride film; the step of forming an SiO2 film as the gate insulating film of a transistor constituting the first circuit; and the step of forming a gate electrode material layer for the transistor constituting the first circuit on the gate insulating film, wherein the gate insulating film and gate electrode material layer of the transistor constituting the first circuit are formed in processes different from those in which the gate insulating film and gate electrode material layer of the transistor constituting the second circuit are formed.
The method preferably has the following characteristics:
(f) The gate insulating film of the transistor constituting the first circuit has a thickness of 5 nm or more and the gate insulating film of the transistor constituting the second circuit has a thickness of less than 5 nm.
(g) The method further comprises the step of patterning the gate electrode material layer of the transistor constituting the first circuit and the gate electrode material layer of the transistor constituting the second circuit by using a single mask, wherein the gate electrode of the transistor constituting the first circuit and the gate electrode of the transistor constituting the second circuit are processed simultaneously.
Furthermore, the second object of the invention is accomplished by providing a method of manufacturing a semiconductor device with an interface circuit operating on a first power supply voltage and exchanging signals and data with an external device, and an internal circuit operating on a second power supply voltage lower than the first power supply voltage, comprising: the step of forming an oxynitride film of nitrogen-added SiO2 as the gate insulating film of the transistor constituting the internal circuit on the main surface of a semiconductor substrate; the step of forming a first gate electrode material layer of the transistor constituting the internal circuit on the oxynitride film; the step of forming a mask on an area in which the internal circuit is to be formed and removing the oxynitride film and the first gate electrode material layer in an area in which the interface circuit is to be formed to expose the main surface of the semiconductor substrate; the step of forming an SiO2 film as the gate insulating film of the transistor constituting the interface circuit on the main surface of the exposed semiconductor substrate; the step of forming a second gate electrode material layer of the transistor constituting the interface circuit on the gate insulating film; and the step of patterning the first and second gate electrode material layers by using a single mask and forming the gate electrodes of the transistor constituting the internal circuit and the transistor constituting the interface circuit.
The method preferably has the following characteristics:
(h) The gate insulating film of the transistor constituting the interface circuit has a thickness of 5 nm or more and the gate insulating film of the transistor constituting the internal circuit has a thickness of less than 5 nm.
(i) The method further comprises the step of forming element isolating regions at the main surface of the semiconductor substrate before the formation of the oxynitride film.
(j) The method further comprises the step of introducing impurities into the semiconductor substrate and forming a source/drain region after the step of forming the gate electrodes of the transistor constituting the internal circuit and the transistor constituting the interface circuit.
With the manufacturing methods described above, because the gate insulating film and gate electrode material layer of the transistor constituting the first circuit (interface circuit) are formed in processes different from those in which the gate insulating film and gate electrode material layer of the transistor constituting the second circuit (internal circuit) are formed, the gate insulating film of the MOSFET constituting the first circuit is made of a pure oxide film (SiO2), and the gate insulating film of the MOSFET constituting the second circuit is made of an oxynitride film, not only the problem of penetration of boron through the MOSFET constituting the second circuit is avoided, but a decrease in the current driving capability due to the appearance of the interface level in the MOSFET constituting the first circuit is prevented. Therefore, it is possible to form a high-speed semiconductor device.
When the gate insulating film of the MOSFET constituting the first circuit (interface circuit) is formed thicker than 5 nm and the gate insulating film of the MOSFET constituting the second circuit (internal circuit) is formed thinner than 5 nm, this suppresses the problem of deterioration of the characteristic because of the influence of nitrogen and the problem of penetration of boron more effectively.
In addition, when the gate electrode material layer of the MOSFET constituting the first circuit (interface circuit) and the gate electrode material layer of the MOSFET constituting the second circuit (internal circuit) are patterned simultaneously using a single mask, this makes it possible to process the gate electrode of the MOSFET constituting the first circuit and the gate electrode of the MOSFET constituting the second circuit simultaneously, which minimizes the complexity of manufacturing processes.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.